Referred to Clinical Biochemistry, East Surrey Hospital, Redhill, Surrey RH1 5RH

Alternative names, keywords


Samples required

Clotted blood (gold cap, 5 mL tube), pre-dose (trough). Smaller tubes are available for paediatric samples.

Note significant diurnal variation - sampling time in relation to dose is important.

4 days to steady state.

Test indications

There is no value in routinely measuring valproate in epilepsy patients. Serum concentrations are no better than dose as a guide to clinical effect, and toxic effects do not show a clear relationship to serum concentration.

 Valproate should only be measured:

1. If there is an issue of compliance with the medication. Assessment of compliance may be quite difficult given that some people have rapid metabolism and can appear non-compliant if the drug level is used as a measure of compliance.

2. If the patient has taken a possible overdose of valproate.

3. When the patient is being treated with valproate for mania or bipolar affective disorder (> 750mg/day). A fasting, trough sample will be required.

Reference range

50 - 100 mg/L

Toxicity is increasingly likely above 100 mg/L but not certain.

Turnaround time

Referral lab quotes turnaround time of 1 day, however additional time must be allowed for packing, dispatch and delivery of sample, and return and processing of results.


Biochemistry (Referrals)